In this paper, we describe the design and implementation of a multi-tier architecture to support environmental research portal. This architecture demonstrates the successful integration of web server, application server, database server, reports server, data warehousing, data mining and simulation models. It achieves high scalability through load balancing, and high reliability through simulation resuming. The load balancing feature is implemented based on simulation completion time prediction. The simulation resuming feature is implemented using Java transaction service
(JTS/JTA). The architecture also integrates simulation sharing and other features to support scientific collaboration among scientists. A scientific simulation, NOM, is used to demonstrate the effectiveness of the architecture.